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Alteration of global nitrogen (N) and phosphorus (P) cycles to support livestock and crop production is the most significant driver of global nutrient surpluses. Losses of excess nutrients to the environment contribute to eutrophication of aquatic systems, leading to harmful algal blooms (HABs), hypoxia, and fish kills. Livestock and dairy production are directly linked to the acceleration of eutrophication via nutrient losses from animal manure. Lake Champlain has been experiencing HABs since the 1970s, and a total maximum daily load (TMDL) is in place to reduce P loading to the lake, with much of the reduction in P load being required to come from the agricultural sector. It is critical to understand nutrient movement and the impact of a changing regional climate in manure-based agricultural watersheds, as dairy farming is the primary agricultural sector in Vermont. Additionally, studying agricultural management practices to mitigate P losses is imperative to meet the target P load reductions set forth by the TMDL. The first portion of this thesis analyzes seasonal differences in nutrient movement in two manure-based agricultural watersheds in the Vermont Lake Champlain Basin (VT LCB) with varying extent of agricultural land use. The results show that the spring and summer had the smallest seasonal loads of total P (TP) and dissolved P (DP) in runoff. The smaller summer P loads appear to be related to periods of drought, while the smaller P loads in the spring are likely related to less manure P built up in the watershed that could be transported to surface waters. Approximately 40% of the cumulative TP load and 43% of the cumulative DP load was discharged from the watersheds in the fall. The increased fall TP and DP loads were likely due to the application of manure across the watersheds during this period. The data suggest that soil erosion is relatively less dominant as a driver of watershed P discharge during times when manure was available for transport post-application (e.g., fall and summer), and more closely linked to watershed P loss during times when less new manure was available (e.g., spring). The results suggest better management of manure application rates and timing as well as increased implementation of agricultural management practices are needed to address increased P transport throughout the year, and especially during the fall. The second portion of this thesis assesses the efficacy of edge-of-field (EOF) iron-based filters for P removal. In-field agricultural management practices such as no-till management and cover cropping target reductions in TP, but do not effectively address DP. EOF filters are a promising management practice for reducing DP losses. Storm runoff at the inlet and outlet of one subsurface and two surface EOF filters was monitored for 10 months. The subsurface filter proved very effective for soluble reactive P (SRP) and TP removal, removing 99% of cumulative SRP load and 91% of TP load from monitored events. The surface filters had varied results, with the east surface filter removing 19% of SRP load and 72% of TP load, and the west surface filter removing 52% of SRP load and having no effect on TP load. The findings highlight the importance of filter sizing and design to minimize the impact of sediment loading and preferential flow pathways on surface EOF filter performance. The study provides early evidence that tile drain filters are a highly effective management strategy for mitigating SRP and TP losses from agricultural fields.
This monograph presents the proceedings of the 2002 Spring Symposium sponsored by the Lake Champlain Research Consortium, hosted by the Missisquoi Bay Watershed Corporation. The book examines this common body of water shared by Canada and the US, and summarizes knowledge of the dynamics of this system with a primary focus on land use, water management, and bridging the gap between researchers and the public.
Published by the American Geophysical Union as part of the Water Science and Application Series, Volume 1. Lake Champlain in Transition: From Research Toward Restoration synthesizes research studies on the chemistry, biology, atmospherics, hydrodynamics, hydrology, land use, and management of Lake Champlain and its basin. Additional studies define the cultlural, social, and economic pressures on the lake's ecosystemm. The volume presents research results on lake sediment toxicity and its effect on benthic and aquatic species. Trophic levels were studied, from the impacts of nitrogen and phosphorus on phytoplankton to multiple "trophic cascades" and management implications. Phosphorus loading and subsequent eutrophication was examined by looking at comprehensive loading budgets, a whole-lake mass-balance model, and subsequent management schemes. This comprehensive research effort was undertaken to develop a management plan devoted to preserving the lake ecosystem, and the volume will interest environmental planners and managers as well as limnologists and hydrologists.
Nonpoint source pollution by phosphorus and sediment is a wide-spread problem across the United States and specifically in Vermont and the Lake Champlain Basin. Best management of nonpoint source loading will likely involve a combination of land use and stream channel modifications, but few studies have comprehensively examined the relative importance of land use, streambank instability, and soil phosphorus. Thus, it is important to understand the associations between these characteristics, as well as their overall, relationship to watershed nutrient loading dynamics. The main objectives of this study were (1) to examine the impacts of land use at the watershed and near-stream scales on total suspended solids (TSS), total phosphorus (TP), and soluble reactive phosphorus (SRP), (2) to explore the links between geomorphic condition and phosphorus and sediment concentrations and loads throughout the watershed and at different spatial scales, and (3) to investigate the importance of soil phosphorus concentrations in stream banks in contributing to the overall phosphorus load. TP, SRP, and TSS samples were collected from eight sites located at tributary junctures and one site at the mouth of Hungerford Brook, a 50 km2 watershed in the Lake Champlain Basin, under storm and baseflow conditions. Rapid geomorphic assessment (RGA) scores, land use, and soil phosphorus concentrations were collected for reaches upstream of sampling locations. Both nested and unnested design multivariate modeling was used to evaluate the importance of characteristics in the individual subwatersheds (unnested) or the entire upstream watershed (nested). SRP, TP, and TSS were predicted as both concentrations and instantaneous loads, using raw quantifications of subwatershed characteristics as well as these same characteristics standardized by the area of agriculture in the subwatershed. Correlation coefficients and principal components analysis were used to select variables that were used in Akaike information criterion (AIC) model selection and stepwise regression. Unnested variables used were agriculture, agriculture in a streamside buffer, proportion of corn, slope, channel degradation, and soil phosphorus. For the nested design, agriculture, agriculture in the buffer, channel aggradation, RGA score, and soil phosphorus concentrations were used. Best fit models were selected based on AICc scores and overall model R2. n ANOVA was also performed on the percent difference between storm flow concentrations and average baseflow concentrations. Results indicate that phosphorus and sediment transport occurs mainly during storm events and concentrations greatly exceed state water quality standards. Concentrations of SRP and TP were significantly lower at the mouth of Hungerford Brook than in upstream subwatersheds, indicating that deposition and storage are occurring in this downstream part of the watershed. SRP concentrations appear to be best explained by agriculture in the riparian buffer, while TP and TSS are influenced by agricultural land use at multiple spatial scales. Agricultural land use was associated with increased stream instability. These findings suggest that additional phosphorus and sediment management, targeted at increasing stream stability and reducing impacts from agriculture, are needed in order to reduce the overall load traveling to Lake Champlain.